Process for the manufacture of alpha highly-valuable cast iron



Patented Mar. 19, 1929.

UNITED STATES PATENT OFFICE.

EUGEN PIWOWARSKY, OF AACHEN, GERMANY, ASSIGNOR '10 EDELGUSSVERBAND G. M. B. H., OF BERLIN-DAHLEM, GERMANY.

PROCESS FOR THE MANUFACTURE OF A HIGHLY-VALUABLE CAST IRON.

No Drawing. Application filed February 11, 1926, Serial No. 87,681, and in Germany February 21, 1925.

It is known that the qualities of cast iron essentially depend on the form and quantity of the graphite included therein. The finer its division and the smaller the quantity of included coarse graphite, the better the mechanical qualities of the cast iron will be.

It has-already been tried to obtain systematically such a cast iron, either by regulating its cooling down or b decreasing the total amount of included carbon or by regulating the chemical composition of the iron. All these processes, however, have shown to be unsuccessful, expensive and applicable only under special circumstances.

This invention is based on the following statements, which have been confirmed by numerous observations.

By heating cast iron over its melting point the carbon contained therein. has more and more the tendency to be bound at the subseuent solidification in the form of carbide. low it has been found that at certain temperatures which depend principally on the chemical composition of the iron the formation of iron carbide amounts to a maximum and that, by exceeding thisdimit of temperature the carbon will separate out at the subsequent solidification essentially in the form of finely divided graphite. The proportlon of bound carbon to free carbon which is obtained by heating the cast iron to difierent temperatures will be understood from the following example:

A cast iron contained:

lower tern eratures the tendency to separate out the car on essentially in the form of finely distributed graphite.

According to this'invention a highl valuable cast iron including finely ivlded graphite is obtained by heating the iron for a certain number of degrees which depends on the special conditions, for instance for 100 to 200 C. over that temperature above which the formation of carbide decreases whereas the formation of graphite increases.

A suitable manner of proceeding consists in heating a certain quantity of iron above said limit of temperature and then mixing this quantity of iron with another quantity of iron which is heated to its'melting point or little higher. Various'observations have shown and theabove given example confirms that also the carbon of an iron which is heated little above its melting point consists essentially of graphite; the latter is, however, very viscous at this temperature and, in consequence thereof, it cannot be cast. Now, if a slightly molten iron is mixed with a superheated iron, a product can be obtained which contains the graphite in the desired quantity and in the finest distribuion.

By the new process firstly the great advantage is obtained that one is nearly independent of the composition of the treatedmaterial from which a highly valuable iron is to be obtained. A further advantage consists in the high tendency of the iron obtained by this process to solidify under separation of graphite even if exposed to influences which would cause general cast iron to plunge, that is to show hard white parts. The iron treated according to this process is therefore especially suitable to be cast in permanent molds of steel, iron or other metal, for instance in a mold which is used in the centrifugal action, since it is not necessary to glow the product as it was hitherto in most cases. By using the new process it is furthermore possible to obtain an iron with graphitic structure from such materials which'are poor in silicon and carbon and rich in manganese, Finally an essential advantage results from the fact that it is not necessary to superheat the total amount of the treated iron, but it is sufficient to highly heat only a part of it and to mix this part with the other slightly molten iron.

The cast iron obtained in the above described manner canbe used with particular advantage to produce highly valuable malleable castings, as it contains in spite ofits white solidification such a considerablequantity of nuclei which favour the formation of graphite that, after a half to four-fifths of the usual duration of annealing, a highly valuable malleable casting is obtained. The annealing temperature itself is held at about 850 to 875 C., with respect to the known rates of temperature of increased number of nuclei (over 800 C.) and of increased velocity of crystallization (below 800 6.). After a short annealing and a subsequent very slow cooling down an excellent malleable casting with the finest distribution of carbon is obtained.

The herein described thermal treatment of the molten metal has also in the case of iron poor in carbon, steel-like iron or steel a considerable influence on the formation of struc ture and thereby on the physical and mechanical qualities of the iron.

What I claim and desire to secure by Letters Patent of the United States is 1. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being substantially higher than the temperature of solidification.

'2. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification.

3. A process for the production of iron which comprises heating liquid iron above that temperature. above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification, and mixing the so treated iron with slightly molten iron.

4. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification, and casting the iron thus obtained in a permanent mold.

5. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperatemperature of solidifi'catiom-mixing the so treated iron before casting with" slightly molten iron, and casting the iron thus obtained in a permanent mold. k

6. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification, to obtain therefrom a highly valuable malleable casting by a relatively short annealing operation. 7. A process for the production of iron which comprises heating liquid iron above that temperature above which the formation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification, and mixing the so treated iron with slightly molten iron to obtain from said mixture a highly valuable malleable casting by a relatively short annealing operation.

8. A process for obtaining steel from iron which comprises heating liquid iron poor in carbon above that temperature above which theformation of carbide will decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification. 9. A process for obtaining steel from iron which comprises mixing a slightly molten iron poor in carbon with an iron heated above that temperature above which the formation of carbidewill decrease whereas the formation of graphite will increase, this temperature being about 300 to 550 higher than the temperature of solidification.

10. The process of treatingmolten castiron which ordinarily upon solidification would contain the major part of the carbon in coarse graphitic form, comprising the step of heating the molten metal to a temperature upward of approximately 1400 (1., in order to cause the metal upon solidification to contain the major part of the carbon in finely graphitic form, and then casting.

11. The method of producing gray cast iron which comprises heating the liquid iron to a temperature upwardly of 100 C. above that at which the iron carbide reaches a maximum and the graphite content begins to increase.

Prof. Dr. lug. EUGEN PIWOWARSKY. 

